The present invention relates to a two axis linear motor for carrying the objective lens in an optical head in an optical recording system of the type in which a laser beam is used to record and play back information optically from a rotating disk containing optical media.
It is well known in the art of the optical recording that an objective lens, as carried by the optical head in an optical recording device, must be moved continuously to focus the laser beam passing through an objective lens to the optical media because of continuous variations in the distance from the lens to the rotating disk as a result of mechanical wobble in the drive system. Even a very slight amount of wobble in the disk will cause the laser beam to be out of focus and, of course, correct focus is critical to this recording technique. If the laser beam is not properly focused, the beam power density will not be high enough to accomplish writing on the media.
Optical heads are known of a type in which a voice coil structure moves an armature in which an objective lens is mounted for movement towards and away from the optical media disk. The optical head is carried by an arm which provides for coarse position control. In addition, it is also known that it is desirable to have a fine position control to move the objective lens inwardly and outwardly in the radial direction with respect to the disk in order to correct minor tracking errors for the particular recording track on which it is desired to focus the objective lens. An optical read device is known in which both focusing movement and inward and outward tracking movement is achieved in the same device. This device is described in European Patent Office Publication No. 0 002 547 published on June 27, 1979. This publication shows separate coil winding and magnet structure combinations for both the tracking movements and for the focusing movements. When separate suspensions were used for tracking and focus in previous designs, unacceptable mechnical coupling existed between the two motions.
It is an object of the present invention to provide an improved two axis linear motor for use in an optical recording head for carrying an objective lens in an optical recording system.